1. Field of the Invention
The present invention relates to a method of forming barrier ribs for manufacturing display panels, such as PDPs (Plasma Display Panel) and PALCs (Plasma Address Liquid Crystal), having barrier ribs for dividing a display area thereof, and to a green sheet or green tape therefor.
PDPs are characterized by excellent visibility and ability to display at high speeds, and are attracting attentions toward high quality TV (high-vision). Toward broadening PDP applications, the manufacturing technologies are being developed for adaptation for higher precision and larger screen displays.
2. Related Arts
The surface-discharge PDPs, under marketing as color-display devices, have barrier ribs for each column to define an interior discharge space of a matrix display. The barrier ribs serve to prevent discharge coupling and cross-talk in color representation from occurring between adjacent columns. The barrier ribs like this are made of a low-melting glass through the manufacture process of providing a predetermined pattern of a barrier-rib material layer on a substrate and sintering the substrate thus processed at a temperature of 400.degree. C. to 600.degree. C. and around.
In recent years, a sand blasting technique adapted for higher precision is broadly utilized in place of the screen-printing method, to form a predetermined pattern of the barrier-rib material layer. In this method, a low-melting glass paste is first printed over an entire surface of the substrate instead of a barrier-rib pattern, or a green tape or green sheet is adhered thereto in a manner disclosed in Japanese Unexamined Patent Publication No. Hei 8 (1996)-255510, thereby providing the barrier-rib material layer on the substrate. On the barrier-rib material layer, a mask for carving is then made of a photosensitive resist by using a well-known photolithography technique. Then a polisher is applied by blasting to carve portions (unmasked portions) of the barrier-rib material layer uncovered with the mask for carving. After carving, the mask for carving is removed by swelling treatment or the like before a sintering process.
Meanwhile, where forming barrier ribs by the sand blasting method, it is possible to prevent against excessively carving the barrier-rib material layer in a depth direction by providing a low-melting glass layer as an underlying layer of the barrier-rib material layer to be carved in a manner giving a carve rate lower than that of the barrier-rib material layer. In particular, when barrier ribs are formed after arranging electrodes on the substrate, the underlying layer has a role to protect the electrode thus formed. Also, there may be a case that the underlying layer functions as a dielectric layer to provide a desired electric characteristics, thus constituting an essential structural element.
Conventionally, the carve-resistive underlying layer has been formed through printing and sintering a low-meting glass paste applied over the entire surface. After forming the underlying layer, barrier ribs are formed, as mentioned above, through the process of forming the barrier-rib material layer, forming the mask for carving, performing sand blasting, removal of the mask for carving, and sintering.
In the conventional method of forming barrier-ribs, however, there has encountered a difficulty in giving an even thickness of the barrier-rib material layer throughout the display area upon printing a paste over the entire surface. Also, there has been a necessity of several times repetition of printing layers one over another in order to increase the thickness up to approximately 200 .mu.m, thus raising another problem of increasing the number of process steps. On the other hand, it is possible for a lamination method including a process of adhering the green sheet to form an even thickness of the barrier-rib material layer, requiring only several seconds of adhering operating time. However, the green sheet contains organic ingredients, such as a binder and a plasticizer, and is hence difficult to be carved in an adhered state as it is. That is, there is a necessity of burning out the organic ingredient so as to change the material into a readily-carvable quality after adhesion of the material. This requires a sintering process also in forming the barrier-rib material layer, in addition to the sintering for forming the underlying layer and the sintering after the carve process. Thus, the barrier-rib formation requires totally three times of sintering processes. It requires at least several hours for sintering, and further several hours if a cooling time period is included. Thus, there has been a problem that a greatly increased total time is required to form barrier ribs when adopting the lamination technique. The increase in number of times of sintering is not preferred from the viewpoint of PDP thermal profiles.
In addition, the conventional method involves another problem that, during removing the mask for carving made of the photosensitive resist material, the barrier-rib material layer tends to be chipped during stripping the swelled mask for carving from the patterned barrier-rib material layer. It can be considered to burn out the mask for carving during sintering the barrier-rib material layer without stripping away the mask for carving. However, this raises a difficulty in selecting a material for the mask for carving, because the material has to fulfill the condition such that the material is completely burnt out by the sintering process.